Methods to deliver fluids on a well site with variable solids concentration from solid slurries

ABSTRACT

The invention discloses a storable composition for oilfield application including a slurry of a carrier fluid and a particulate blend made of proppant; the particulate blend comprising at least a first amount of particulates having a first average particle size between about 100 and 5000 μm and at least a second amount of particulates having a second average particle size between about three and twenty times smaller than the first average particle size; such that a packed volume fraction of the particulate blend exceeds 0.74 and the particulate blend volume is sufficient to substantially avoid settling of the particulate in the carrier fluid.

FIELD OF THE INVENTION

The invention relates to methods for treating well bores. More particularly, the invention relates to methods for delivery of fluids with variable solids concentration within.

BACKGROUND

The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.

Hydrocarbons (oil, condensate, and gas) are typically produced from wells that are drilled into the formations containing them. For a variety of reasons, such as inherently low permeability of the reservoirs or damage to the formation caused by drilling and completion of the well, the flow of hydrocarbons into the well is undesirably low. In this case, the well is “stimulated” for example using hydraulic fracturing, chemical (usually acid) stimulation, or a combination of the two (called acid fracturing or fracture acidizing).

In hydraulic and acid fracturing, a first, viscous fluid called the pad is typically injected into the formation to initiate and propagate the fracture. This is followed by a second fluid that contains a proppant to keep the fracture open after the pumping pressure is released. Granular proppant materials may include sand, ceramic beads, or other materials. These types of materials are well known to those skilled in the art. In “acid” fracturing, the second fluid contains an acid or other chemical such as a chelating agent that can dissolve part of the rock, causing irregular etching of the fracture face and removal of some of the mineral matter, resulting in the fracture not completely closing when the pumping is stopped. Occasionally, hydraulic fracturing can be done without a highly viscosified fluid (i.e., slick water) to minimize the damage caused by polymers or the cost of other viscosifiers.

In gravel packing, gravel is placed in the annulus of screen and formation/casing to control formation sand production. A carrier fluid is used to transport gravel from the surface to the formation where the gravel has to be placed. Typically two types of carrier fluids are used. The first is a brine with a low concentration of gravel (11 b per gal of brine) and the second is a viscous fluid with higher concentration of gravel (51 b per gal of brine). Several types of viscosifiers are used to increase the viscosity of the fluid. These include polymers such as HEC, Xanthan, Guar and guar derivatives, etc. and viscoelastic surfactants. In a combination of gravel packing and hydraulic fracturing, referred to in the industry as frac and pack, a viscous fluid is typically pumped to create/propagate a hydraulic fracture by pumping a pad fluid followed by a slurry (fluid containing proppant) to completely fill the hydraulic fracture. In this type of treatment it is critical to completely fill the fracture to the point where no additional propagation occurs and the remaining slurry is “squeezed” into the hydraulic fracture with increasing pressure. This is referred to in the industry as a tip screenout (TSO). This is important because the next step of the frac and pack is to shift the flow of the fluid being pumped to now perform the gravel pack part of the operation. This technique is known by those skilled in the art.

Conventionally, the components are mixed at the surface prior to being pumped into the well with a pumping device. Further peripheral devices are present such as a blender, a particulates hauler, fluid storage tank(s), and other devices understood in the art. Water from the storage tank is mixed with a viscosifying agent or various additives to create the base fracturing fluid. Proppant or particulates are added to the fracturing fluid from a conveyor at the blender, or are added directly by the blender (this method is on-the-fly). In some gravel pack operations, and may be done rarely in frac and pack treatments, the base fluid and particulates (proppant) are batch-mixed before being pumped in the wellbore.

The mixing of the components has to be done on site and prior to pumping into the well, because the transport and storage of already prepared solid fluids (with proppant, gravel, or other particulate material) suffer from a lot of drawbacks. A common problem that occurs during pre-mixed slurry transport or storage is the setting of solids due to difference in densities of the fluid and the solid particles. If the solids start settling before the fluid is used, the fluid will need to be remixed prior to use. If use of such settled fluid was tried, several problems can occur including screen outs, incomplete gravel packs, wellbore blockage, stuck tools etc. To reduce the settling rate, the carrier fluid is typically viscosified using polymers or surfactants. However, increasing the viscosity of the fluid can increase the friction pressure significantly and renders the fluid not pumpable. An alternative would be to add fiber to the fluid mixture (FiberFRAC—of Schlumberger). In this case the fluid viscosity essentially stays the same but the proppant suspension is significantly better. Other methods could be to use lighter density proppant so that the density between fluid and proppant is minimized so that proppant suspension is improved. The best case would be where the fluid and the proppant are equal density.

Compositions and methods disclosed herewith offer a new way to deliver fluid with variable solid concentrations on well site.

SUMMARY

In a first aspect, a storable composition for oilfield application is disclosed. The composition includes a slurry of a carrier fluid and a particulate blend made of proppant; the particulate blend comprising at least a first amount of particulates having a first average particle size between about 100 and 5000 μm and at least a second amount of particulates having a second average particle size between about three and twenty times smaller than the first average particle size; such that a packed volume fraction of the particulate blend exceeds 0.74 and the particulate blend volume is sufficient to substantially avoid settling of the particulate in the carrier fluid. The packed volume fraction or packing volume fraction (PVF) is the fraction of the solid content volume to the total volume content. In another embodiment, the first amount of particulates has a first average particle size between about 100 and 2000 μm.

In a second aspect, a method of servicing a well on a well site is disclosed. The method includes the steps of defining a type of treatment needed for the well; estimating for the type of treatment a concentration and volume of proppant needed; and providing on the well site the needed concentration of proppant from a ready-to-use composition made of a slurry of a carrier fluid and a particulate blend made of proppant.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an illustration of the storable composition according to one embodiment.

DETAILED DESCRIPTION

At the outset, it should be noted that in the development of any actual embodiments, numerous implementation-specific decisions must be made to achieve the developer's specific goals, such as compliance with system and business related constraints, which can vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time consuming but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure.

The description and examples are presented solely for the purpose of illustrating embodiments of the invention and should not be construed as a limitation to the scope and applicability of the invention. In the summary of the invention and this detailed description, each numerical value should be read once as modified by the term “about” (unless already expressly so modified), and then read again as not so modified unless otherwise indicated in context. Also, in the summary of the invention and this detailed description, it should be understood that a concentration range listed or described as being useful, suitable, or the like, is intended that any and every concentration within the range, including the end points, is to be considered as having been stated. For example, “a range of from 1 to 10” is to be read as indicating each and every possible number along the continuum between about 1 and about 10. Thus, even if specific data points within the range, or even no data points within the range, are explicitly identified or refer to only a few specific, it is to be understood that inventors appreciate and understand that any and all data points within the range are to be considered to have been specified, and that inventors possession of the entire range and all points within the range disclosed and enabled the entire range and all points within the range.

The following definitions are provided in order to aid those skilled in the art in understanding the detailed description.

The term “treatment”, or “treating”, refers to any subterranean operation that uses a fluid in conjunction with a desired function and/or for a desired purpose. The term “treatment”, or “treating”, does not imply any particular action by the fluid.

The term “fracturing” refers to the process and methods of breaking down a geological formation and creating a fracture, i.e. the rock formation around a well bore, by pumping fluid at very high pressures (pressure above the determined closure pressure of the formation), in order to increase production rates from a hydrocarbon reservoir. The fracturing methods otherwise use conventional techniques known in the art.

FIG. 1 is a schematic diagram of a storable composition 106 used in methods to deliver fluids on a well site with variable solids concentration from solid slurries. The storable composition 106 includes a slurry of a carrier fluid 202 and a particulate blend made of proppant; the particulate blend comprising at least a first amount of particulates 204 having a first average particle size between about 100 and 5000 μm and at least a second amount of particulates 206 having a second average particle size between about three and twenty times smaller than the first average particle size.

According to one embodiment, the storable composition is used as a fracturing fluid and the carrier fluid has optionally a viscosifying agent. The carrier fluid includes any base fracturing fluid understood in the art. Some non-limiting examples of carrier fluids include hydratable gels (e.g. guars, poly-saccharides, xanthan, hydroxy-ethyl-cellulose, etc.), a cross-linked hydratable gel, a viscosified acid (e.g. gel-based), an emulsified acid (e.g. oil outer phase), an energized fluid (e.g. an N₂ or CO₂ based foam), and an oil-based fluid including a gelled, foamed, or otherwise viscosified oil. Additionally, the carrier fluid may be a brine, and/or may include a brine.

The viscosifying agent may be any crosslinked polymers. The polymer viscosifier can be a metal-crosslinked polymer. Suitable polymers for making the metal-crosslinked polymer viscosifiers include, for example, polysaccharides such as substituted galactomannans, such as guar gums, high-molecular weight polysaccharides composed of mannose and galactose sugars, or guar derivatives such as hydroxypropyl guar (HPG), carboxymethylhydroxypropyl guar (CMHPG) and carboxymethyl guar (CMG), hydrophobically modified guars, guar-containing compounds, and synthetic polymers. Crosslinking agents based on boron, titanium, zirconium or aluminum complexes are typically used to increase the effective molecular weight of the polymer and make them better suited for use in high-temperature wells.

Other suitable classes of polymers effective as viscosifying agent include polyvinyl polymers, polymethacrylamides, cellulose ethers, lignosulfonates, and ammonium, alkali metal, and alkaline earth salts thereof. More specific examples of other typical water soluble polymers are acrylic acid-acrylamide copolymers, acrylic acid-methacrylamide copolymers, polyacrylamides, partially hydrolyzed polyacrylamides, partially hydrolyzed polymethacrylamides, polyvinyl alcohol, polyalkyleneoxides, other galactomannans, heteropolysaccharides obtained by the fermentation of starch-derived sugar and ammonium and alkali metal salts thereof.

Cellulose derivatives are used to a smaller extent, such as hydroxyethylcellulose (HEC) or hydroxypropylcellulose (HPC), carboxymethylhydroxyethylcellulose (CMHEC) and carboxymethycellulose (CMC), with or without crosslinkers. Xanthan, diutan, and scleroglucan, three biopolymers, have been shown to have excellent particulate-suspension ability even though they are more expensive than guar derivatives and therefore have been used less frequently, unless they can be used at lower concentrations.

In other embodiments, the viscosifying agent is made from a crosslinkable, hydratable polymer and a delayed crosslinking agent, wherein the crosslinking agent comprises a complex comprising a metal and a first ligand selected from the group consisting of amino acids, phosphono acids, and salts or derivatives thereof. Also the crosslinked polymer can be made from a polymer comprising pendant ionic moieties, a surfactant comprising oppositely charged moieties, a clay stabilizer, a borate source, and a metal crosslinker. Said embodiments are described in U.S. Patent Publications US2008-0280790 and US2008-0280788 respectively, each of which are incorporated herein by reference.

The viscosifying agent may be a viscoelastic surfactant (VES). The VES may be selected from the group consisting of cationic, anionic, zwitterionic, amphoteric, nonionic and combinations thereof. Some non-limiting examples are those cited in U.S. Pat. Nos. 6,435,277 (Qu et al.) and 6,703,352 (Dahayanake et al.), each of which are incorporated herein by reference. The viscoelastic surfactants, when used alone or in combination, are capable of forming micelles that form a structure in an aqueous environment that contribute to the increased viscosity of the fluid (also referred to as “viscosifying micelles”). These fluids are normally prepared by mixing in appropriate amounts of VES suitable to achieve the desired viscosity. The viscosity of VES fluids may be attributed to the three dimensional structure formed by the components in the fluids. When the concentration of surfactants in a viscoelastic fluid significantly exceeds a critical concentration, and in most cases in the presence of an electrolyte, surfactant molecules aggregate into species such as micelles, which can interact to form a network exhibiting viscous and elastic behavior.

In general, particularly suitable zwitterionic surfactants have the formula:

RCONH—(CH₂)_(a)(CH₂CH₂O)_(m)(CH₂)_(b)—N⁺(CH₃)₂—(CH₂)_(a′)(CH₂CH₂O)_(m′)(CH₂)_(b′)COO⁻

in which R is an alkyl group that contains from about 11 to about 23 carbon atoms which may be branched or straight chained and which may be saturated or unsaturated; a, b, a′, and b′ are each from 0 to 10 and m and m′ are each from 0 to 13; a and b are each 1 or 2 if m is not 0 and (a+b) is from 2 to 10 if m is 0; a′ and b′ are each 1 or 2 when m′ is not 0 and (a′+b′) is from 1 to 5 if m is 0; (m+m′) is from 0 to 14; and CH₂CH₂O may also be OCH₂CH₂. In some embodiments, a zwitterionic surfactants of the family of betaine is used.

Exemplary cationic viscoelastic surfactants include the amine salts and quaternary amine salts disclosed in U.S. Pat. Nos. 5,979,557, and 6,435,277 which are hereby incorporated by reference. Examples of suitable cationic viscoelastic surfactants include cationic surfactants having the structure:

R₁N⁺(R₂)(R₃)(R₄)X⁻

in which R₁ has from about 14 to about 26 carbon atoms and may be branched or straight chained, aromatic, saturated or unsaturated, and may contain a carbonyl, an amide, a retroamide, an imide, a urea, or an amine; R₂, R₃, and R₄ are each independently hydrogen or a C₁ to about C₆ aliphatic group which may be the same or different, branched or straight chained, saturated or unsaturated and one or more than one of which may be substituted with a group that renders the R₂, R₃, and R₄ group more hydrophilic; the R₂, R₃ and R₄ groups may be incorporated into a heterocyclic 5- or 6-member ring structure which includes the nitrogen atom; the R₂, R₃ and R₄ groups may be the same or different; R₁, R₂, R₃ and/or R₄ may contain one or more ethylene oxide and/or propylene oxide units; and X⁻ is an anion. Mixtures of such compounds are also suitable. As a further example, R₁ is from about 18 to about 22 carbon atoms and may contain a carbonyl, an amide, or an amine, and R₂, R₃, and R₄ are the same as one another and contain from 1 to about 3 carbon atoms.

Amphoteric viscoelastic surfactants are also suitable. Exemplary amphoteric viscoelastic surfactant systems include those described in U.S. Pat. No. 6,703,352, for example amine oxides. Other exemplary viscoelastic surfactant systems include those described in U.S. Pat. Nos. 6,239,183; 6,506,710; 7,060,661; 7,303,018; and 7,510,009 for example amidoamine oxides. These references are hereby incorporated in their entirety. Mixtures of zwitterionic surfactants and amphoteric surfactants are suitable. An example is a mixture of about 13% isopropanol, about 5% 1-butanol, about 15% ethylene glycol monobutyl ether, about 4% sodium chloride, about 30% water, about 30% cocoamidopropyl betaine, and about 2% cocoamidopropylamine oxide.

The viscoelastic surfactant system may also be based upon any suitable anionic surfactant. In some embodiments, the anionic surfactant is an alkyl sarcosinate. The alkyl sarcosinate can generally have any number of carbon atoms. Alkyl sarcosinates can have about 12 to about 24 carbon atoms. The alkyl sarcosinate can have about 14 to about 18 carbon atoms. Specific examples of the number of carbon atoms include 12, 14, 16, 18, 20, 22, and 24 carbon atoms. The anionic surfactant is represented by the chemical formula:

R₁CON(R₂)CH₂X

wherein R₁ is a hydrophobic chain having about 12 to about 24 carbon atoms, R₂ is hydrogen, methyl, ethyl, propyl, or butyl, and X is carboxyl or sulfonyl. The hydrophobic chain can be an alkyl group, an alkenyl group, an alkylarylalkyl group, or an alkoxyalkyl group. Specific examples of the hydrophobic chain include a tetradecyl group, a hexadecyl group, an octadecentyl group, an octadecyl group, and a docosenoic group.

The viscosifying agent may be present in lower amount than conventionally is included for a fracture treatment. The loading of a viscosifier, for example described in pounds of gel per 1,000 gallons of carrier fluid, is selected according to the particulate size (due to settling rate effects) and loading that the storable composition 106 must carry, according to the viscosity required to generate a desired fracture geometry, according to the pumping rate and casing or tubing configuration of the wellbore, according to the temperature of the formation of interest, and according to other factors understood in the art.

In certain embodiments, the low amount of a viscosifying agent includes a hydratable gelling agent in the carrier fluid at less than 20 pounds per 1,000 gallons of carrier fluid where the amount of particulates in the storable composition 106 are greater than 16 pounds per gallon of carrier fluid. In certain further embodiments, the low amount of a viscosifier includes a hydratable gelling agent in the carrier fluid at less than 20 pounds per 1,000 gallons of carrier fluid where the amount of particulates in the fracturing slurry 106 are greater than 23 pounds per gallon of carrier fluid. In certain embodiments, a low amount of a viscosifier includes a viscoelastic surfactant at a concentration below 1% by volume of carrier fluid. In certain embodiments, the low amount of a viscosifier includes the carrier fluid with no viscosifier included. In certain embodiments a low amount of a viscosifier includes values greater than the listed examples, because the circumstances of the storable composition conventionally utilize viscosifier amounts much greater than the examples. For example, in a high temperature application with a high proppant loading, the carrier fluid may conventionally indicate a viscosifier at 50 lbs. of gelling agent per 1,000 gallons of carrier fluid, wherein 40 lbs. of gelling agent, for example, may be a low amount of viscosifier. One of skill in the art can perform routine tests of storable composition based on certain particulate blends in light of the disclosures herein to determine acceptable viscosifier amounts for a particular embodiment.

In certain embodiments, the carrier fluid includes an acid. The fracture may be a traditional hydraulic bi-wing fracture, but in certain embodiments may be an etched fracture and/or wormholes such as developed by an acid treatment. The carrier fluid may include hydrochloric acid, hydrofluoric acid, ammonium bifluoride, formic acid, acetic acid, lactic acid, glycolic acid, maleic acid, tartaric acid, sulfamic acid, malic acid, citric acid, methyl-sulfamic acid, chloro-acetic acid, an amino-poly-carboxylic acid, 3-hydroxypropionic acid, a poly-amino-poly-carboxylic acid, and/or a salt of any acid. In certain embodiments, the carrier fluid includes a poly-amino-poly-carboxylic acid, and is a trisodium hydroxyl-ethyl-ethylene-diamine triacetate, mono-ammonium salts of hydroxyl-ethyl-ethylene-diamine triacetate, and/or mono-sodium salts of hydroxyl-ethyl-ethylene-diamine tetra-acetate. The selection of any acid as a carrier fluid depends upon the purpose of the acid—for example formation etching, damage cleanup, removal of acid-reactive particles, etc., and further upon compatibility with the formation, compatibility with fluids in the formation, and compatibility with other components of the fracturing slurry and with spacer fluids or other fluids that may be present in the wellbore. The selection of an acid for the carrier fluid is understood in the art based upon the characteristics of particular embodiments and the disclosures herein.

The storable composition includes a particulate blend made of proppant. Proppant selection involves many compromises imposed by economical and practical considerations. Criteria for selecting the proppant type, size, size distribution in multimodal proppant selection, and concentration is based on the needed dimensionless conductivity, and can be selected by a skilled artisan. Such proppants can be natural or synthetic (including but not limited to glass beads, ceramic beads, sand, and bauxite), coated, or contain chemicals; more than one can be used sequentially or in mixtures of different sizes or different materials. The proppant may be resin coated (curable), or pre-cured resin coated. Proppants and gravels in the same or different wells or treatments can be the same material and/or the same size as one another and the term proppant is intended to include gravel in this disclosure. In some embodiments, irregular shaped particles may be used. International application WO 2009/088317 discloses a method of fracturing with a slurry of proppant containing from 1 to 100 percent of stiff, low elasticity, low deformability elongated particles. US patent application 2007/768393 discloses proppant that is in the form of generally rigid, elastic plate-like particles having a maximum to minimum dimension ratio of more than about 5, the proppant being at least one of formed from a corrosion resistant material or having a corrosion resistant material formed thereon. In general the proppant used will have an average particle size of from about 0.15 mm to about 4.76 mm (about 100 to about 4 U.S. mesh), preferably from about 0.15 mm to about 3.36 mm (about 100 to about 6 U.S. mesh), more preferably from about 0.15 mm to about 4.76 mm (about 100 to about 4 U.S. mesh), more particularly, but not limited to 0.25 to 0.42 mm (40/60 mesh), 0.42 to 0.84 mm (20/40 mesh), 0.84 to 1.19 mm (16/20 mesh), 0.84 to 1.68 mm (12/20 mesh) and 0.84 to 2.38 mm (8/20 mesh) sized materials. Normally the proppant will be present in the slurry in a concentration from about 0.12 to about 0.96 kg/L, or from about 0.12 to about 0.72 kg/L, or from about 0.12 to about 0.54 kg/L. Also, there are slurries where the proppant is at a concentration up to 16 PPA (1.92 kg/L). If the slurry is foamed the proppant is at a concentration up to 20 PPA (2.4 kg/L). The storable composition is not a cement slurry composition.

The storable composition is a slurry comprising particulate materials with defined particles size distribution. On example of realization is disclosed in U.S. Pat. No. 7,784,541, herewith incorporated by reference in its entirety. In certain embodiments, the selection of the size for the first amount of particulates is dependent upon the characteristics of the propped fracture, for example the closure stress of the fracture, the desired conductivity, the size of fines or sand that may migrate from the formation, and other considerations understood in the art. In certain further embodiments, the selection of the size for the first amount of particulates 204 is dependent upon the desired fluid loss characteristics of the first amount of particulates as a fluid loss agent, the size of pores in the formation, and/or the commercially available sizes of particulates of the type comprising the first amount of particulates.

In certain embodiments, the selection of the size of the second amount of particulates 206 is dependent upon maximizing a packed volume fraction (PVF) of the mixture of the first amount of particulates and the second amount of particulates. The packed volume fraction or packing volume fraction (PVF) is the fraction of solid content volume to the total volume content. A second average particle size of between about seven to ten times smaller than the first amount of particulates contributes to maximizing the PVF of the mixture, but a size between about three to twenty times smaller, and in certain embodiments between about three to fifteen times smaller, and in certain embodiments between about three to ten times smaller will provide a sufficient PVF for most storable compositions. Further, the selection of the size of the second amount of particulates is dependent upon the composition and commercial availability of particulates of the type comprising the second amount of particulates. For example, where the second amount of particulates comprise wax beads, a second average particle size of four times (4×) smaller than the first average particle size rather than seven times (7×) smaller than the first average particle size may be used if the 4× embodiment is cheaper or more readily available and the PVF of the mixture is still sufficient to acceptably suspend the particulates in the carrier fluid. In certain embodiments, the particulates combine to have a PVF above 0.74 or 0.75 or above 0.80. In certain further embodiments the particulates may have a much higher PVF approaching 0.95.

In certain embodiments, the storable composition 106 further includes a third amount of particulates 208 having a third average particle size that is smaller than the second average particle size. In certain further embodiments, the storable composition 106 may have a fourth or a fifth amount of particles. Also in some embodiments, the same chemistry can be used for the third, fourth, or fifth average particle size. Also in some embodiments, different chemistry can be used for the same third average particle size: e.g. in the third average particle size, half of the amount is PLA and the other half is PGA. For the purposes of enhancing the PVF of the storable composition 106, more than three or four particles sizes will not typically be required. For example, a four-particle blend including 217 g of 20/40 mesh sand, 16 g or poly-lactic acid particles with an average size of 150 microns, 24 g of poly-lactic acid particles with an average size of 8 microns, and 53 g of CaCO₃ particles with an average size of 5 microns creates a particulate blend 111 having a PVF of about 0.863. In a second example, a three-particle blend wherein each particle size is 7× to 10× smaller than the next larger particle size creates a particulate blend having a PVF of about 0.95. However, additional particles may be added for other reasons, such as the chemical composition of the additional particles, the ease of manufacturing certain materials into the same particles versus into separate particles, the commercial availability of particles having certain properties, and other reasons understood in the art.

Also, the particulate blend volume is sufficient to substantially avoid settling of the particulate in the carrier fluid. In certain embodiments, the storable composition includes a degradable material or a viscosifier material embodied as a third, fourth or a fifth average particle size. For example, the particulates may be completely made from degradable material or viscosifier material, inactive in a first state and able to increase the viscosity of the carrier fluid in a second state. The activation from the first state to the second state is made by a trigger. In certain embodiments, the trigger is time, pH or temperature. One example of realization is disclosed in U.S. patent application Ser. No. 12/551,081 herewith incorporated by reference in its entirety. The viscosifier may be used to reduce or even avoid the settling rate. The settling rate can be avoided with specially chosen volume particulate blend, or by selecting appropriate chemistry with increase in the viscosity of the carrier fluid along storage of the composition 106.

In certain embodiments, the degradable material includes at least one of a lactide, a glycolide, an aliphatic polyester, a poly (lactide), a poly (glycolide), a poly (ε-caprolactone), a poly (orthoester), a poly (hydroxybutyrate), an aliphatic polycarbonate, a poly (phosphazene), and a poly (anhydride). In certain embodiments, the degradable material includes at least one of a poly (saccharide), dextran, cellulose, chitin, chitosan, a protein, a poly (amino acid), a poly (ethylene oxide), and a copolymer including poly (lactic acid) and poly (glycolic acid). In certain embodiments, the degradable material includes a copolymer including a first moiety which includes at least one functional group from a hydroxyl group, a carboxylic acid group, and a hydrocarboxylic acid group, the copolymer further including a second moiety comprising at least one of glycolic acid and lactic acid.

In certain embodiments, the viscosifier material includes an acid soluble polymer which is added to the storable composition along with an acid precursor. The acid precursor can be one of the degradable particles in the slurry. The acid soluble polymer is in the form of a solid particle at surface conditions. As the acid soluble polymers are solid particles having an average particle size, they can be included in the optimization process of PVF. Along storage of the slurry, the acid precursor releases acid and changes the pH of the carrier fluid. The acid soluble polymer particles dissolve in the fluid increasing the viscosity of the fluid. Examples of acid soluble polymers include chitosan or chitosan derivatives such as the N-carboxybutyl chitosan or the N-carboxymethyl chitosan, polyimides such as the examples described in U.S. Pat. Nos. 6,379,865 or 6,559,245, incorporated herewith by reference, copolymers of vinyl pyridine as those described in U.S. Pat. No. 7,294,347, incorporated herewith by reference, or copolymers of acrylic and/or methacrylic acid or mixture of those polymers.

In certain embodiments, the viscosifier material includes an acid soluble polymer which is added to the storable composition along with an encapsulated acid or acid precursors. The acid soluble polymer is of the type as disclosed in paragraph above. The acid required for triggering the dissolution of the acid soluble polymer is added to the mixture as the encapsulated acid or acid precursors. The encapsulated acid or acid precursors release acid after some time in the slurry. Examples include encapsulated PLA, PGA other hydroxy acids, citric, glycolic, maleic acid/anhydride etc. Encapsulated material can be a solid polymer acid precursor. Examples of solid polymer acid precursors that may be used include homopolymers of lactic acid, glycolic acid, hydroxybutyrate, hydroxyvalerate and epsilon caprolactone, random copolymers of at least two of lactic acid, glycolic acid, hydroxybutyrate, hydroxyvalerate, epsilon caprolactone, L-serine, L-threonine, L-tyrosine, block copolymers of at least two of polyglycolic acid, polylactic acid, hydroxybutyrate, hydroxyvalerate, epsilon caprolactone, L-serine, L-threonine, L-tyrosine, homopolymers of ethylenetherephthalate (PET), butylenetherephthalate (PBT) and ethylenenaphthalate (PEN), random copolymers of at least two of ethylenetherephthalate, butylenetherephthalate and ethylenenaphthalate, block copolymers of at least two of ethylenetherephthalate, butylenetherephthalate, ethylenenaphthalate and combinations of these. Some of the encapsulated material may include acrylics, halocarbon, polyvinyl alcohol, Aquacoat® aqueous dispersions, hydrocarbon resins, polyvinyl chloride, Aquateric® enteric coatings, hydroxypropyl cellulose (HPC), polyvinylacetate phthalate, hydroxypropyl methyl cellulose (HPMC), polyvinylidene chloride, hydroxylpropyl methyl cellulose phthalate (HPMCP), proteins, Kynar®, fluoroplastics, rubber (natural or synthetic), caseinates, maltodextrins, shellac, chlorinated rubber, silicone, polyvinyl acetate phtalate (e.g. Coateric®) coatings, microcrystalline wax, starches, coating butters, milk solids, stearines, polyvinyl dichloride (Daran®) latex, molasses, sucrose, dextrins, nylon, surfactants, Opadry® coating systems, Surelease® coating systems, enterics, paraffin wax, Teflon® fluorocarbons, Eudragits® polymethacrylates, phenolics, waxes, ethoxylated vinyl alcohol, vinyl alcohol copolymer, polylactides, zein, fats, polyamino acids, fatty acids, polyethylene gelatin, polyethylene glycol, glycerides, polyvinyl acetate, vegetable gums and polyvinyl pyrrolidone.

In some embodiments, the carrier fluid may optionally further comprise additional additives, including, but not limited to, acids, fluid loss control additives, gas, corrosion inhibitors, scale inhibitors, catalysts, clay control agents, biocides, friction reducers, combinations thereof and the like. For example, in some embodiments, it may be desired to foam the storable composition using a gas, such as air, nitrogen, or carbon dioxide.

In an exemplary embodiment, a method of servicing a well on a well site includes defining a type of treatment needed for the well; estimating for the type of treatment a concentration and a volume of proppant needed; and providing on the well site the needed concentration of proppant from the storable composition which is ready to use. By this way a delivery of variable concentration of proppant where the source of proppant is a pumpable slurry is achieved.

The method can further include estimating for the type of treatment an updated concentration and an updated volume of proppant needed; and providing on the well site the needed updated concentration of proppant. As well, it is possible that the step of estimating for the type of treatment the updated concentration and the updated volume of proppant needed be repeated during the treatment.

By bringing multiple storable ready-to-use compositions on the well site, it is possible to achieve different proppant concentrations. For example, it may be necessary to start with one proppant concentration and step up another proppant concentration as the treatment progresses.

In another exemplary embodiment a method of fracturing a well on a well site, includes estimating for the fracturing treatment a concentration and a volume of proppant needed; providing on the well site the needed concentration of proppant from a ready-to-use composition made of a slurry of a carrier fluid and a particulate blend made of proppant; and fracturing the well. Also, it is possible to bring multiple storable ready-to-use compositions on the well site. For example, it may be necessary to start with lower proppant concentration and step up to higher proppant concentration as the treatment progresses. This would be similar logic to conventional fracturing treatments. This way we would also have the opportunity to vary the concentrations of the second, third, and additional additives to potentially achieve a more optimum benefit.

A possible application would be to change the mode of fracturing in shales, by delivering the same or higher proppant concentration than current slick water treatments, by pumping alternative slugs of a flowable high solids slurry and of a clean friction reducing fluid without increasing the total friction in the pipe. The near wellbore effects such as perforation friction and tortuosity will be the same or reduced by the properties of this new pumpable slurry. This would allow the field to have flexibility in the use of other non-conventional equipment. A treatment pumped this way would be able to maintain the same or greater hydrostatic pressure than what is being pumped nowadays in a typical slick water, and without the risk of increasing the friction pressure that could result if a high solids content (and thus viscous) fluid would be pumped at high rate, or without the need of reducing the pump rate as would be required to ensure pumpable pressures (pressures lower that the maximum allowable surface pressure as dictated by the wellbore construction, wellhead, surface pumping equipment, or other weaker point) at surface with such a high solids content fluid.

The storable composition may be used for carrying out a variety of subterranean treatments, including, but not limited to, drilling operations, fracturing treatments, and completion operations (e.g., gravel packing). In some embodiments, the storable composition may be used in treating a portion of a subterranean formation. In certain embodiments, a storable composition may be introduced into a well bore that penetrates the subterranean formation as a treatment fluid. For example, the treatment fluid may be allowed to contact the subterranean formation for a period of time. In some embodiments, the treatment fluid may be allowed to contact hydrocarbons, formations fluids, and/or subsequently injected treatment fluids. After a chosen time, the treatment fluid may be recovered through the well bore. In certain embodiments, the treatment fluids may be used in fracturing treatments.

The method is also suitable for gravel packing, or for fracturing and gravel packing in one operation (called, for example frac and pack, frac-n-pack, frac-pack, STIMPAC (Mark of Schlumberger) treatments, or other names), which are also used extensively to stimulate the production of hydrocarbons, water and other fluids from subterranean formations. These operations involve pumping a slurry of fluid and propping agent/material in hydraulic fracturing or gravel (materials are generally the same as the proppants used in hydraulic fracturing) in gravel packing. In low permeability formations, the goal of hydraulic fracturing is generally to form long, high surface area fractures that greatly increase the magnitude of the pathway of fluid flow from the formation to the wellbore. In high permeability formations, the goal of a hydraulic fracturing treatment is typically to create a short, wide, highly conductive fracture, in order to bypass near-wellbore damage done during drilling and/or completion operations, to ensure good fluid communication between the reservoir and the wellbore and also to increase the surface area available for fluids to flow into the wellbore.

In certain embodiments, the storable composition may be used for providing some degree of sand control in a portion of the subterranean formation. In the sand control embodiments, the treatment fluid is introduced into the well bore that penetrates the subterranean formation such that the particulates form a gravel pack in or adjacent to a portion of the subterranean formation.

In a example, a conventional slick water treatment pumped today (typically this could be 100,000 gallons of fluid using 1 gpt (gallons per 1,000 gallons) of polyacrylamide and pumping an average additional 30,000 gallon of pad, and an average of 1 ppa (pounds of proppant added to one gallon of fluid) proppant during the prop stage) is replaced by a storable composition. The treatment is characterized by a treatment fluid averaging at least 1 ppa, formulated with alternating slugs of clean fluid and flowable proppant slurry, so that the length of each of the proppant slugs is at the most 1/50 of the total wellbore volume. The proppant concentration for the storable composition is up to 75-80% by volume of the fluid.

Nowadays, for these jobs proppant is typically pumped either continuously at 1 ppa max, or alternatively as proppant ramps up to 2 ppa followed by some flush stages of clean fluid averaging 1 ppa total proppant in the prop stages. In the case of the proppant ramps followed by clean fluid flush, the later is at least a volume of fluid bigger than the wellbore volume, and the volume of the prop stages are several times bigger than the wellbore volume.

The foregoing disclosure and description of the invention is illustrative and explanatory thereof and it can be readily appreciated by those skilled in the art that various changes in the size, shape and materials, as well as in the details of the illustrated construction or combinations of the elements described herein can be made without departing from the spirit of the invention. 

1. A storable composition for oilfield application, comprising a slurry of a carrier fluid and a particulate blend made of proppant; the particulate blend comprising at least a first amount of particulates having a first average particle size between about 100 and 5000 μm and at least a second amount of particulates having a second average particle size between about three and twenty times smaller than the first average particle size; such that a packed volume fraction of the particulate blend exceeds 0.74.
 2. The composition of claim 1, wherein the carrier fluid comprises a viscosifying agent and water.
 3. The composition of claim 1, wherein the carrier fluid comprises a friction reducer agent and water.
 4. The composition of claim 1, wherein the carrier fluid comprises an acid and water.
 5. The composition of claim 1, wherein the particulate blend comprises a degradable material.
 6. The composition of claim 1, wherein the particulate blend comprises a viscosifier material.
 7. The composition of claim 6, wherein the viscosifier material is an acid soluble polymer which increases viscosity of the composition when in acid pH.
 8. The composition of claim 7, wherein the acid soluble polymer is chitosan, chitosan derivative, polyimide, copolymer of vinyl pyridine, copolymer of acrylic and/or methacrylic acid or a mixture thereof.
 9. The composition of claim 7, wherein the particulate blend comprises an acid precursor.
 10. The composition of claim 9, wherein the acid precursor is encapsulated.
 11. The composition of claim 1, wherein the particulate blend further includes a third amount of particulates having a third average particulate size that is smaller than the second average particulate size.
 12. The composition of claim 1, wherein the packed volume fraction of the particulate blend exceeds 0.8.
 13. A method of servicing a well on a well site, comprising: preparing an oilfield composition comprising a slurry of a carrier fluid and a particulate blend made of proppant; the particulate blend comprising at least a first amount of particulates having a first average particle size between about 100 and 5000 μm and at least a second amount of particulates having a second average particle size between about three and twenty times smaller than the first average particle size; such that a packed volume fraction of the particulate blend exceeds 0.74; and delivering the oilfield composition to the well.
 14. (canceled)
 15. The method of claim 13, wherein the particulate blend volume is sufficient to substantially avoid settling of the particulate in the carrier fluid.
 16. (canceled)
 17. (canceled)
 18. The method of claim 13, wherein the concentration by volume of proppant in the composition is between 74% and 95%.
 19. The method of claim 18, wherein the concentration by volume of proppant in the composition is between 75% and 80%.
 20. The method of claim 13, wherein said serving the well is selected from the list consisting of: hydraulic fracturing, drilling, gravel packing, sand control and other completion or workover types of treatments.
 21. The method of claim 13, wherein the particulate blend comprises a viscosifier material able to reduce settling of the particulate in the carrier fluid.
 22. The method of claim 21, wherein the viscosifier material is an acid soluble polymer which increases viscosity of the composition when in acid pH.
 23. The method of claim 22, wherein the acid soluble polymer is chitosan, chitosan derivative, polyimide, copolymer of vinyl pyridine, copolymer of acrylic and/or methacrylic acid or a mixture thereof.
 24. The method of claim 22, wherein the particulate blend comprises an acid precursor.
 25. The method of claim 24, wherein the acid precursor is encapsulated.
 26. (canceled)
 27. (canceled)
 28. (canceled)
 29. The method of claim 13, wherein the particulate blend volume is sufficient to substantially avoid settling of the particulate in the carrier fluid.
 30. The method of claim 13, wherein the particulate blend further includes a third amount of particulates having a third average particulate size that is smaller than the second average particulate size.
 31. The method of claim 20, wherein said serving the well is hydraulic fracturing.
 32. The method of claim 20, wherein said serving the well is gravel packing.
 33. The method of claim 20, wherein said serving the well is drilling.
 34. The method of claim 20, wherein said serving the well is performing a frac and pack treatment. 